New chloroethylating agents are being investigated as possible replacements for anticancer chloroethylnitrosoureas (ClEtNUs). New compounds are derived which would produce less diversity of reactions than the C1EtNus, yet retain the reactions that are essential for antitumor activity. To this end, 2-chloroethylmethylsulfonylmethanesulfonate ('ClEtSoSo', NSC 338947) is being investigated. The chemical structure of this compound suggests that it would be a more selective chloroethylating agents than ClEtNUs. Studies of human cells in culture revealed that ClEtSoSo produces the same DNA lesions as ClEtNUs, namely interstrand crosslinks, DNA-protein crosslinks and low frequencies of both DNA strand breaks and alkali-labile lesions. These lesions were assayed in human cells by alkaline elution methods. As with ClEtNUs, interstrand crosslinks by ClEtSoSo were prevented in cells rich in guanine-06-alkyltransferase, and cell survival was enhanced. DNA alkylation products are being isolated by HPLC and will be identified by mass spectrometry in order to compare the range of DNA base adducts produced by the different chloroethylating agents.